Glass sealing compositions containing aluminum titanate

ABSTRACT

A crystallizable fusion-type glass sealing composition, such as lead borosilicate or lead-zinc-borate solder glass, having incorporated therein from about 1 to about 25 percent by weight of aluminum titanate; which solder glass is useful in sealing TV bulbs, in electronics sealing applications and in other instances where the sealing of a glass surface to another surface, such as glass, can be accomplished at a temperature sufficiently low as not to damage any sensitive or delicate electronic parts closely spaced from the surfaces being sealed.

United States Patent Veres 1 Feb. 29, 1972 [54] GLASS SEALINGCOMPOSITIONS 3,061,664 10/!962 Kegg ..106/53 X CONTAINING ALUMINUMTITANATE 3,250,631 5/1966 Lusher ..106/47' 3,258,350 6/1966 Martin etal. ..106/47 lnvemofi Frank Wm, Toledo, 01110 3,486,871 12/1969 Martin..106/53 x- [73] Assignee: Owens-Illinois, Inc. OTHER PUBLICATIONS [22]led: Sept 1969 Ceramic Raw Materials, in Ceramic industry Magazine, 86,21 Appl. No.: 860,433 Jan. 11

Related US. Application Data Primary Examiner-Tobias E. Levow AssistantExaminer-W. R. Satterfield [63] Continuation-in-part of Ser. No.790,465, Jan. 10, A"0mey Edward J Holler and Richard Dem:e

i969, abandoned.

' [57] ABSTRACT [52] US. Cl. ..161/193, 65/36, 106/39 DV,

10 /43 105/53 117/124 T, 7/125 117/129 A crystallizable fusion-typeglass sealing composition, such as 1 1 1 lead borosilicate orlead-zinc-borate solder glass, having in- 51 Int. Cl. ..B32b 17/06, C03c3/04 corporated therein from about 1 to about 25 Percent y [58] Field fSearch "106]391349 53 23/51; weight of aluminum titanate; which solderglass is useful in 61/1 192, 193, 117/125 129, 124 65/36 sealing TVbulbs, in electronics sealing applications and in other instances wherethe sealing of a glass surface to another [56] References cued surface,such as glass, can be accomplished at a temperature sufficiently low asnot to damage any sensitive or delicate elec- UNlTED STATES PATENTStronic parts closely spaced from the surfaces being sealed.

Claypoole ..106/39 X 11 Claims, No Drawings GLASS SEALING COMPOSITIONSCONTAINING ALUMINUM TITANATE This is a continuation in part of mayapplication Ser. No. 790,465, filed Jan. 10, 1969 and entitled GLASSSEALING COMPOSITIONS, and now abandoned.

This invention relates to glass sealing compositions and moreparticularly to crystallizable glass sealing compositions suitable foreffectively sealing a glass surface to another sur-' face includingglass, metal, ceramic and like surfaces.

While the easiest method for sealing two glass surfaces together is byfusion of the glass, for glasses used in the electronics industry, thetemperature to which the surfaces must be subjected in order to softeneach surface sufficiently to cause it to flow and fuse with the glass ofthe other surface is extremely high with respect to the sensitive partsinvolved. Depending upon the particular glass composition, thistemperature may be as high as 2,2002,600 F. If the glass surfaces to befused are part of an article containing delicate and sensitivecomponents, such as a cathode-ray tube having a cathodoluminescentsurface deposited on the faceplate and a cathode-ray electronic gunassembly within the funnel portion of the tube, it is necessary to sealthe surfaces of the glass faceplate and glass funnel at a temperaturelower than that which would detrimentally affect the heat-sensitivecomponents within the articles and/or soften or collapse the glassenvelopes. To achieve this sealing, solder glasses such as leadborosilicate and lead-zinc-borate glasses, for example, have beendeveloped by the art. Such solder glasses have a softening point whichis considerably lower than the annealing temperature of the glasssurfaces being sealed so that the glass surfaces may be safely subjectedto this lower temperature for a period of time sufficient to cause thesolder glass to soften and flow into and fill the space between thesurfaces to form a durable seal upon cooling of the parts, withoutdetrimentally affecting the contents of the article being sealed.

A thermally crystallizable sealing glass is applied by flowing orbrushing a slurry comprising the finely divided sealing glass particlesin an organic vehicle onto one or both of the glass surfaces to besealed. The surfaces are then placed in contact with each other andsubjected to a temperature above the softening point of the sealingglass, causing it to flow and wet the surfaces to be sealed whilevolatilizing the vehicle. Since this temperature is below the annealingtemperature of the surfaces being sealed, there is no distortion ordeformation of the glass surfaces, nor is there any collapse of theglass article, such as a glass envelope, being sealed. The sealingtemperature is maintained for a sufficient period of time to accomplishthe desired crystallization, and the sealed surfaces are then cooled toambient temperature.

It is also known that the relationship of the sealing glass and theglassbeing sealed has to be such that the solder glass can perform itssealing function without creating any detrimental stresses between theseal and the surfaces being sealed. The most satisfactory results aregenerally obtained when the coefficient of thermal contraction of thesolder glass composition is less than the coefficient of thermalcontraction of the surfaces being sealed, so that the sealing glass isin a moderate degree of compression. However, the solder glasses knownto the art that have the desired characteristics enumerated below havecoefficients of thennal contraction which are at best very slightlylower than or, worse, slightly greater than that of the surfaces beingsealed. As a consequence, the sealing glass is in a state of very lowcompression or is in tension and, as such, the product is morevulnerable to failure than if the sealing glass were in a moderatedegree of compression. The use of refractory oxides and silicates, suchas zircon, to modify the expansion characteristics of solder glass so asto makesuch expansion characteristics more nearly like those of theglass being sealed is also known. However, while these additives doaffect the expansion characteristics of the solder glass, they alsoadversely affect other properties of the solder glass, such as flowproperties, crystallization times, etc., and thus make the solder glassunsuitable for certain applications.

Therefore, it is an object of the present invention to provide a sealingglass having an additive therein; which additive lowers the contractioncharacteristics of the sealing glass but does not adversely affect theother properties of the sealing glass.

It is a further object of this invention to provide a sealing glasscomposition containing an additive wherein the additive does notadversely affect the flow characteristics of the sealing glass, does notadversely affect the length of time it takes for the sealing glass tocrystallize and does not decrease the temperature range within which theglass remains in its glassy state.

In attaining the objects of this invention, the principal featureresides in the use of a small amount of aluminum titanate which isincorporated in the sealing glass and which lowers the coefficient ofthermal contraction of the sealing glass without adversely affecting theother important properties of the sealing glass.

Other objects, features and advantages will become more apparent fromthe following description of the invention.

It has been found that aluminum titanate can be added to sealingglasses, of which crystallizable solder glasses are an example, withoutmaterially affecting the basic properties of the glass other thansufficiently lowering the coefficient of thermal contraction so that itis lower than that of the glass being sealed. Among the solder glassesfor which the present invention is applicable are the lead borosilicateand lead-zincborosilicate glasses having a sealing temperature below thedeformation temperature of the material to which they are to be sealed.

It should be appreciated that the amount of aluminum titanate selectedfor addition to the sealing glass can be varied over a fairly broadrange. Thus, even as little as l-2 percent by weight thereof isreflected in a lowering of the coefficient of contraction. Increasingamounts, particularly above 25 percent by weight, generally will have aneffect on the viscosity of the glass; that is, the viscosity willincrease. However, for some applications, the increase in viscosity isnot a significant factor. Furthermore, even where viscosity is a factorin the specific application, the particular glass can be selected orbatch ingredients added, deleted or adjusted to accommodate the presenceof the aluminum titanate in order to achieve the desired tailoredlowering of the coefficient of contraction.

Best results are obtained, particularly with glasses containingappreciable amounts of lead oxide, when up to about 25 weight percentand, preferably, from about five to about 20 weight percent of finelydivided aluminum titanate is incorporated within the finely dividedsealing glass composition and the mixture agitated until a uniformblending or dispersion of the additive occurs. Thus, the sealing glasscomposition should be selected which has thermal contractioncharacteristics close to that of the glass surface being sealed. Byadding the aluminum titanate to the sealing glass in a predeterminedamount, the coefficient of thermal contraction of the sealing glass isaccordingly lowered, but the other properties of the glass, includingflow properties and crystallization times, remain substantiallyunchanged. While a relatively large amount of aluminum titanate canbe'present in the sealing glass composition, and the coefl'rcient ofthermal contraction of the sealing glass lowered even more, the abilityof the sealing glass to flow and wet the surfaces being sealed graduallydiminishes at the glass-sealing temperature. However, this ability toflow is till greater than in a sealing glass containing zircon as theadditive.

Sealing glass compositions particularly suitable for purposes of thisinvention come within the following formulation wherein the ingredientsare set forth in weight percent:

TABLE l Ingredients PhO ZnO 5-20 8,0, 5-20 -4 Al,0 0-3 BaO 0-5 CaF, 0-2CaO 0 5 MgO 0-5 SnO, 0-4 Aluminum titanate up to 25 Colorants 0-2 Oxidessuch as K 0, CuO, si o, and similar fluxes, colorants and the like maybe included in the sealing glass in minor amounts which will notmaterially affect the basic characteristics of the glass.

Aluminum titanate is prepared by ball-milling 5,555 parts by weight ofaluminum (Alcoa A-lO) and 3,514.5 parts by weight of TiO (Frit makersgrade obtained from Titanium v Alloy Manufacturing Company) for 26 hoursin an aluminafortified porcelain jar mill using alumina-fortifiedporcelain balls as grinding media. The alumina and the titania were morethan 99.5 percent pure with traces of a few other ingredients therein.The mixture was then placed in a platinum crucible; the crucible wasplaced in a gas-fired crucible furnace which was maintained at aslightly oxidized condition, i.e., 0.5 to 1 percent excess 0 at atemperature of 2,700 F. for 40 hours. The crucible was then removed fromthe furnace and allowed to cool to room temperature. The sinteredproduct was then ball-milled for 31% hours until a fine powder wasformed having an average particle size of 200 mesh. An analysis of theproduct showed a trace of alpha-alumina and a very minor quantity ofrutile. Substantially all of the mixture was aluminum titanate.

it has been found that aluminum titanate suitable for the presentinvention can be produced in accordance with the above method by usingfrom 55 to 65 parts by weight alumina and from 45 to 35 parts by weightTiO without any discemible change in essential properties of the sealingglass mixture.

A comparison of applicants sealing glass composition containing aluminumtitanate with a zircon-containing solder glass was made. Zircon, likealuminum titanate, is essentially alkali-free. Also, zircon is one ofthe most chemically inert and one of the most solution-resistantadditives in the solder glass art. A solder glass which has enjoyedwidespread commercial acceptance was used for the comparison tests. Theglass has the following composition:

Several samples were prepared using the above sealing glass andrespectively l%, 2.5%, and by weight aluminum titanate, 1% and 5% byweight milled zircon and 1% and 5% by weight Superpax A; the latterbeing the trademark for a well-known finely ground zircon.

The sealing glass compositions having the additives uniformly blendedtherein were then tested to ascertain (l) the glassy range, (2) the timerequired at a firing temperature of 450 C.-before crystallization tookplace, (3) the seal stress which occurred when each glass was sealed toa reference glass and (4) the flow characteristics of the glass at thesealing temperature.

The flow characteristics of the glass were measured by the standardButton Flow Test used by suppliers and consumers of solder glass in thecolor television industry. A 10 g. sample of the glass is pressed at2,000 p.s.i. into an annular tablet having a diameter of 0.75 inches.The tablet is then heated at the rate of 7.5 C. per minute to atemperature of 450 C. and is held at this temperature for one hour. Thediameter of the fused button is then measured after the button hascooled. This measurement is an index of the flowability of the glass.

In measuring the time it takes for the sealing glass to crystallize onceit has reached a temperature of 450 C., the glass is subjected to aDifferential Thermal Analysis (DTA). The finely divided sealing glass isheated at the rate of 10 C. per hour to a temperature of 450 C. As soonas this temperature is reached, the time is noted. The glass is thenmaintained at 450 C. When crystallization of the glass occurs, there isan exothermic reaction. By means of thermocouples placed within thesample, the sharp peak or rise in the solder glass temperature is notedas soon as crystallization occurs. Upon completion of crystallization,the temperature drops suddenly. The length of time at which the glasswas held at 450 C. until the temperature peaked is the measure of thetime of crystallization. The longer the time at the sealing temperaturebefore crystallization occurs, the less stringent the temperaturecontrol problem is to the user.

The stresses which are formed when the sealing glass is sealed to aglass surface are measured by the Rod Seal Stress Test. A glass rod witha known thermal contraction coefficient and having a diameter of aboutone-quarter inch has two of its opposite surfaces ground flat andparallel adjacent to one end thereof. A mixture of the sealing glassbeing tested and a liquid vehicle serving as a fugitive or temporarybinder therefor (nitrocellulose in arnylacetate, for example) is appliedto the end of the glass rod and the rod and sealing glass are fired at450 C. for one hour. The stress at the interface is determined bymeasuring the retardation of polarized light. When the sealing glassundergoes a smaller total contraction than does the reference glass, thereference glass exerts a force on the sealing glass, thus placing thesealing glass in a state of compression. When the sealing glasscontracts to a greater extent than does the reference glass, thereference glass exerts an outward pull on the sealing glass, thusplacing the sealing glass in a state of tension. In the Rod Seal StressTestswhich are conducted to ascertain the information set forth in Table3, infra, the glass rods had the composition expressed in weight percentof 63.5% SiO 4.4% A1 0 7.3% Na O, 5.2% CaO/MgO, 7.5% 8210, l0.3% K 0,with minor amounts of Sb O AS203, PbO, Li O, CeO F, Rb 0, O and Fe Omaking up the remainder of the composition. The glass had a fibersoftening point of 690 C., an annealing point of 488 C., a strain pointof 450 C., a coefficient of thermal expansion of 98.5 l0"/C. LQflQQZaQLan a s e ft ientp the l C QSZLQELQf 1 12* 1,9.-UQlfmmannsalins P n toThe glassy range of the sealing glass, i.e., the temperature rangewithin which the sealing glass remains in a fused or molten state, isascertained by the Gradient Boat Test. Finely divided sealing glass isplaced into a gradient boat which is then placed into a gradient f$rnacewherein different parts of the boat are simultaneously subjected todifferent temperatures for a period of time with the lowest temperatureapplied to one end of the boat and the temperature progressivelyincreasing with the highest temperature being applied at the other endof the boat. After one hour, the gradient boat is removed fromtlief$mace and the contentsallowed to cool for visual examination. Thatportion of the sealing glass subjected to the low temperatures isusually still in powdery form, but that portion adjacent thereto whichhas been subjected to a higher temperature has become sintered. infurther examining the gradient test specimen, the temperature at whichthe sealing glass turned from sintered powder to fused glass can bereadily ascertained visually. This is known as the glassy edge (GE)temperature. The point at which the sealing glass turned from fusedglass to crystalline ceramic is also readily ascertained visually. Thistemperature is referred to as the crystalline edge (CE) temperature. Thedifference in temperature (C.) between the glassy edge and thecrystalline edge is the glassy range of the sealing glass.

It is important to have the glassy range as broad as possible. The timewithin which the sealing glass can be kept at the sealing temperaturebefore crystallization occurs should also be as long as possible. Thisbecomes important in the process of sealing cathode-ray tubes, such astelevision tubes, wherein temperature differentiations across the tubemay exist during the sealing process. If the crystallization time is tooshort, part of the bulb may be having the sealing glass undergodevitrification or crystallization while the other part of the bulb mayhave the sealing glass still in a glassy state. If the glassy range istoo narrow, it is possible to have the glass crystallize before it hashad an opportunity to completely flow and thoroughly wet the surfaces tobe sealed.

The following table sets forth the comparative data pertaining to theaforementioned sealing glass, per se; the sealing glass containing thevarious amounts of aluminum titanate and the sealing glass containingthe various amounts of zircon and Superpax A.

TABLE 3 sequently, decreases the 5635c: losse seven though the tensilestress in the base glass has correspondingly increased.

The primary purpose of additives is to induce a controlled, moderatelevel of compressive stress in the sealant glass. Test resultssummarized in the above table show that very small amounts of aluminumtitanate significantly increase the com pressive stress in the sealant,that the level of the compressive stress is easily controlled by theamount of additive present and that the aluminum titanate of thisinvention is more effective in inducing compressive stress than thezircon additive known to the prior art. 7

The sealing glass compositions of the present invention, beingessentially alkali-free, are especially suitable for use in thoseelectronic applications where the presence of alkali is known to bedeleterious.

For example, an alkali-free solder glass sealant is necessary toencapsulate microelectronic semiconductor clips in alu- Hi LEQFYQQBQ-W7-,

Time to Rod seal Glassy isother- Button stress Solder glass with percentrange, mul peak, flow, compresby Weight additive 0. minutes inches sionp.s.i.

No additive 59 21 1.12 800 1% aluminum titanate 60 23. 5 1. 10 1, 7002.5% aluminum titanate..." 60 25 1. 10 1,900 4 5% aluminum titanate 5325 1. 07 2, 600 5. 10% aluminum titanate 48 27 1.02 6 1% zircon 50 15 1.07 1, 050 7. 5% zircon 41 9 0. 98 2, 300 8 1% Superpax A 47 13 1. 061,150 9 5% Superpax A 44 9 0.96 1,900

Seal failed due to high stress.

titanate decreases the glassy range of the solder glass by only 6 C., 5percent zircon decreases the glassy range by 18 C.

and 5 percent Superpax A decreases the glassy range by 15 C.

Also, from the above table, it is seen that the presence of the aluminumtitanate unexpectedly increases the time for the sealing glass to reachits isothermal peak (i.e., the time it remains in the fluid state beforeit crystallizes) by as much as 30 percent. This increase in time duringwhich the solder glass is in the liquid state is of importance tocommercial users in that it gives them a greater flexibility in theirsealing processes, particularly in sealing color television picturetubes. Zircon, on the other hand, considerably decreased the time thatthe sealing glass remained the fluid state; the decrease beingapproximately 30 to 60 percent, depending upon whether 1 percent or 5percent milled zircon or Superpax A was present.

Also from the above table, while the flow characteristics of the solderglass, as indicated by the Button Flow Test, are substantiallymaintained when 1 percent or 2% percent aluminum titanate is present,and even when 5 percent aluminum titanate is present, it is to be notedthat the presence of the zircon or the Superpax A materially affectsthese flow characteristics when compared to the same amount of aluminumtitanate. 7

From the foregoing table, it is seen also that the aluminum titanateproduces substantially more of a compressive stress in the sealing glasssealant material than does the corresponding amount of zircon orSuperpax A.

Table 4 below recites the compositional analysis for a preferred glasssealing composition of the present invention.

The above glass has a glassy edge temperature determined by the gradientboat method as described above of 348 C. and a crystal edge temperatureof 382 C. The stresses in the sealing glass as determined by theabove-described Rod Seal Stress Test reveal compression values of 640 to660 p.s.i. (first run) and from 1,500 to 1,550 p.s.i. (second run) at380 C. and 1,550 to 1,650 p.s.i. at 400 C. The flow properties of thesealing glass are fair. The glass rods used in the instant Rod SealStress Tests had a composition expressed in weight per- 7 cent of 70.6%SiO 0.2% B 0 2.0% A1 0 0.3% K 0, 13.4

It has been found in commercial practice that many product Na O, 7.2%CaO, 5.3% MgO, 0.02% As O 1.0% BaO, 0.07% Fe O, and 0.2% $0,. This glasshad a fiber softening point of 735 C., an annealing point of 547 C., astrain point of 504 C., a coefficient of thermal expansion of 83x10in/in/C. (0-300 C.), a coefficient of thermal contraction of 102Xl0'in/in/C. (S4725 C.) and a density of 2.52% EXAMPLE 1 1 Reducing theamount of aluminum titanate in the Example 10 glass to nine percentyielded a sealing glass of the invention having a glassy edgetemperature of 340 C. and a crystalline Final Blend edge temperature 381C. The

revealed compression stresses in the sealing glass ranging from 875p.s.i. to 950 p.s.i. at 400 C. EXAMPLE 12 A glass formulated from thesame base glass as in Example but containing 18 percent aluminumtitanate possessed a glassy edge temperature of 342 C. and a crystallineedge temperature of 384 C. The rod seal stress analysis revealedcompression stresses at 400 C. of 2,500 p.s.i.

A specific compositional analysis representative of a preferred sealingglass composition of particular utility and of the present invention isgiven in Table 5.

TABLE 5 Example '1 3 Ingredients Weight Percent PbO 82.0 ZnO 6.0 8,0,7.0 SiO, 3.0 Ba() 2.0

Total 1000 Aluminum titanate l 1.0 Colorant 0.3

The above glass has a coefficient of thermal contraction compatible withthat of alumina normally about 80-90Xl0' in/in/C. over the range 0-300C. and a sealing temperature of 450 C. or below. The sealing glass hasextremely'desirable flow characteristics whereby sealing and joining ofalumina to other components including alumina is readily accomplished.

The sealing glass composition can be applied by spraying, silkscreening, etc. The assembly is then fired to provide a hermetic seal.

Table 6 contains a recitation of several'sealing glass compositions ofthe invention in which the amount of aluminum titanate is varied.

TABLE 6 Example 14 Example Example 16 Ingredients Weight Percent SiO,2.10 2.10 2.10 3,0 9.98 9.98 9.98 ZnO 15.86 [5.86 15.86

PbO 71.25 71.25 71.25 SnO, 100 L00 1.00

Aluminum titanate 3 5 7 The properties of the sealing glass compositionof Table 6 are given in Table 7.

Good

' Differential thermal analysis (described previously).

Using a transpirent glass rod formed of a glass having the samecomposition as the glass rods described in Example 10.

"'Compression.

5 composition which is selected or formulated to experience fusion,thereby creating the seal at a temperature below the ldecompositiontemperature of the aluminum titanate. This temperature may vary from 750C. to l,300 C. Usually, the base glass should have a sealing temperaturebelow the midpoint in the range indicated to thereby avoid anydeleterious J' effect initiated or caused by any products ofdecomposition of the aluminum titanate. Minor amounts of the latter, ofcourse, may be tolerated so that flexibility exists as to the precisetemperature within the range defined hereinabove.

1 claim:

1. A thermally crystallizable fusion-type glass sealing compositionconsisting essentially of a mixture of:

l. a base sealing glass selected from the group consisting of (a) a leadborosilicate solder glass and (b) a lead-zincborate solder glass and 2.from about 1 to percent by weight of aluminum titanate.

2. A thermally crystallizable fusion-type glass sealant composition asclaimed in claim 1, wherein the amount of aluminum titanate is selectedto impart to the glass sealing composition an increase in the time forthe fused glass to exhibit an isothermal peak.

3. A thermally crystallizable fusion-type glass sealant composition asclaimed in claim 1, wherein the glass is in the fused state and in therange 750 C. to 1,300 C. exhibits flow greater than in the absence ofsaid aluminum titanate.

4. The fusion-type glass sealing composition as defined in claim 1,wherein said sealing glass consists essentially of 70 to l 82 weightpercent PhD, 5 to 20 weight percent ZnO and 5 to 20 weight percent B 05. A fusion-type sealing glass composition having the followingapproximate compositional analysis:

SiO, 3.5%

PbO 80.6%

a 0.. 2.1% Tq al. 100.0%

SiO, 2.10%

ZnO 15.86%

PbO 71.25%

.EQL .a. as a 190% v 5 g Total 100.19%and Aluminum titanate (Al,TiO,) 3to 7% based on said base glass 7. A fusion-type sealing glasscomposition having the following approximate compositional analysis:

.' ZnO 6.0%

. 1 530 2.0% MM W# "wwv Tum Ipfl WM 100.0% '7 Aluminum titanate (AlJiOQ11.0%

8. A fusion-type seal consisting essentially of a fused glass sealanthaving a sealing temperature below the deformation temperature of thematerial to which it is sealed, said glass sealant being selected fromthe group consistingof (a) a lead borosilicate solder glass and (b) alead-zinc-borate solder glass, said fused sealant having therein anamount of from about 1 to 25 percent by weight of aluminum titanate.

9. The fusion-type seal as defined in claim 8, wherein said seal is incompression.

10s A composite ahiikfifiirifig a preformedcompoheht igfid fifisiciedrwmthe group consisting of (a) a featuring a surface formed of a mate ialec from the lead borosilicate solder glass and (b) alead-zinc-boratesolder group glass, m ta C mi and like SUI'faCeS and sealed fglass, saidsealant having distributed therethrough an amount said surface afusion-type seal consisting essentially of a fus ed of from about I to25 percent by weight of aluminum titanate. sealing glass sealant havinga sealing temperature below the 5 1- h composite article as defined inclaim 10 wherein deformation temperature of the said surface of thepreformed Sald Sea] charactenzed by being a State of p c5510". componentto which it is sealed, said glass sealant beiri

2. from about 1 to 25 percent by weight of aluminum titanate.
 2. Athermally crystallizable fusion-type glass sealant composition asclaimed in claim 1, wherein the amount of aluminum titanate is selectedto impart to the glass sealing composition an increase in the time forthe fused glass to exhibit an isothermal peak.
 3. A thermallycrystallizable fusion-type glass sealant composition as claimed in claim1, wherein the glass is in the fused state and in the range 750* C. to1,300* C. exhibits flow greater than in the absence of said aluminumtitanate.
 4. The fusion-type glass sealing composition as defined inclaim 1, wherein said sealing glass consists essentially of 70 to 82weight percent PbO, 5 to 20 weight percent ZnO and 5 to 20 weightpercent B2O3.
 5. A fusion-type sealing glass composition having thefollowing approximate compositional analysis: SiO2 3.5% B2O3 7.5% PbO80.6% ZnO 6.3% BaO 2.1% Total 100.0% Aluminum titanate (Al2TiO5) 11.9%6. A fusion-type sealing glass compositiOn comprising a base glasshaving the following approximate compositional analysis: SiO2 2.10% B2O39.98% ZnO 15.86% PbO 71.25% SnO2 1.00% Total 100.19% and Aluminumtitanate (Al2TiO5) 3 to 7% based on said base glass.
 7. A fusion-typesealing glass composition having the following approximate compositionalanalysis: PbO 82.0% ZnO 6.0% B2O3 7.0% SiO2 3.0% BaO 2.0% Total: 100.0%Aluminum titanate (Al2TiO5) 11.0%
 8. A fusion-type seal consistingessentially of a fused glass sealant having a sealing temperature belowthe deformation temperature of the material to which it is sealed, saidglass sealant being selected from the group consisting of (a) a leadborosilicate solder glass and (b) a lead-zinc-borate solder glass, saidfused sealant having therein an amount of from about 1 to 25 percent byweight of aluminum titanate.
 9. The fusion-type seal as defined in claim8, wherein said seal is in compression.
 10. A composite articlecomprising a preformed component featuring a surface formed of amaterial selected from the group glass, metal, ceramic and like surfacesand sealed to said surface a fusion-type seal consisting essentially ofa fused sealing glass sealant having a sealing temperature below thedeformation temperature of the said surface of the preformed componentto which it is sealed, said glass sealant being formed of a glassselected from the group consisting of (a) a lead borosilicate solderglass and (b) a lead-zinc-borate solder glass, said sealant havingdistributed therethrough an amount of from about 1 to 25 percent byweight of aluminum titanate.
 11. The composite article as defined inclaim 10 wherein said seal is characterized by being in a state ofcompression.